The present invention relates to semiconductor integrated circuits incorporating an A/D converter, and in particular relates to the techniques for effectively reducing the effect of the noise from a digital terminal in combining an analog terminal of the A/D converter with the digital terminal.
In a semiconductor integrated circuit such as a microcomputer or microcontroller incorporating an A/D converter, an analog signal supplied from the outside is converted to a digital signal by the A/D converter, and the digital signal is supplied to a central processing unit (CPU).
Patent Document 1 (Japanese Patent Laid-Open No. 2005-26805) describes a microcomputer incorporating an A/D converter, wherein an analog multiplexer that selects a plurality of analog signals supplied from a plurality of external terminals is coupled to an input terminal. The incorporated A/D converter is configured as a successive approximation type A/D including a comparator circuit in the form of a sample hold circuit, a digital section, a successive approximation register, and a local D-A converter.
On the other hand, as well known, in the semiconductor integrated circuit, an analog terminal is combined with a digital terminal in order to reduce the number of external terminals. For example, in page 7 of Non-Patent Document 1 (Data Sheet of TC94A58FG “Single-chip CD Processor with Built-in Controller”, TOSHIBA CMOS Digital Integrated Circuit Silicon Monolithic, pp. 1-20, 2005-12-7, from http://www.semicon.toshiba.co.jp/docs/datasheet/jp/ASSP/TC94A58FG_ja_datasheet—051207.pdf searched on Jul. 5, 2010 with # search=‘Toshiba CMOS digital integrated circuit silicon monolithic TC94A58FG’), there is a description that four input terminals (analog terminals) of an A/D converter built in one chip processor are combined with I/O port terminals (digital terminals) of an LCD driver. Furthermore, Patent Document 2 (Japanese Patent Laid-Open No. 11-154864) describes that a plurality of analog input terminals of an analog multiplexer coupled to the input terminal of an A/D converter is combined with a multi-bit digital input terminal of a digital multiplexer coupled to the output terminal of the A/D converter.